Implantable drug infusion devices are used to provide patients with a constant and long term dosage or infusion of a drug or any other therapeutic agent. Essentially such device may be categorized as either active or passive.
Active drug or programmable infusion devices feature a pump or a metering system to deliver the drug into the patient's system. An example of such an active drug infusion device currently available is the Medtronic SynchroMed programmable pump. Such pumps typically include a drug reservoir, a peristaltic pump to pump out the drug from the reservoir, and a catheter port to transport the pumped out drug from the reservoir via the pump to a patient's anatomy. Such devices also typically include a battery to power the pump as well as an electronic module to control the flow rate of the pump. The Medtronic SynchroMed pump further includes an antenna to permit the remote programming of the pump. Passive drug infusion devices, in contrast, do not feature a pump, but rather rely upon a pressurized drug reservoir to deliver the drug. Thus such devices tend to be both smaller as well as cheaper as compared to active devices. An example of such a device includes the Medtronic IsoMed.TM.. This device delivers the drug into the patient through the force provided by a pressurized reservoir applied across a flow control unit.
Regardless of whether the device is an active or passive drug infusion device, any such devices present challenges to assemble, in a sufficiently hermetic manner while still using biocompatible materials. These difficulties are further magnified when such a device utilizes micro-electrical mechanical systems (MEMS). MEMS typically are extremely small, and further are constructed from a silicon-glass or silicon-silicon sandwich. In particular, to date, the joining of different types of materials necessary for use of MEMS technology in an implantable infusion device has not been feasible using any other joining techniques other than welding. In the extremely harsh and ceaselessly aggressive environment found in the body, epoxies and other glues, while permitting a mechanical joint to be reliably fashioned, have not permitted that same joint to be assembled in a satisfactorily leak-proof or water tight manner. Over time, most joint seals using glues or epoxies have been found to permit vapor or moisture to be passed through the joint. When dealing with implantable electrical devices, such vapor can have serious, if not catastrophic, consequences. Thus, to date, the use of welds is found to be the most effective method for joining similar as well as disparate materials together in order to assemble the implantable infusion device.
Welding, however, is often difficult to implement when joining different or disparate materials together. Namely, thermal stresses often result through the heating and the cooling of these materials, such stresses often having unintended or unacceptable consequences with regards to other areas of the device. With particular regards to drug infusion devices, it has been a problem to reliably join a drug reservoir to the other fluid handling components through welding. One area where this problem exists in the joining of the drugs reservoir to such a MEMS device. As mentioned above, MEMS typically are of a sandwich construction, and thus the direct welding of a component to them is not possible. Often, it has been necessary to use or more intermediary layers to achieve a bond to the MEMS but which may, in turn later be welded to the drug reservoir, for example. During the weld process, however, often the thermal stresses have caused the joint to be formed with one or more flaws, i.e. buckling (when welding thin membranes), delamination (when welding thin film), cracking (of glasses due to stresses introduced when welding).
It is, thus, the object of the present invention to provide a drug infusion device which permits such a drug reservoir to be coupled to the fluid handling components through welding.